The present invention relates generally to drive train components for automotive, truck, and industrial uses, and more specifically to differentials that permit unequal rotational speeds between driven wheels. In particular, the present invention relates to a yaw control feature for automotive differentials.
The traditional differentials are a well-known component of an automotive drive train. The differential operates to distribute torque evenly between driven wheels, even when the wheels are rotating at different speeds. Initially, the differential was implemented to facilitate cornering of the vehicle and to prevent slip between the inboard wheel and the road surface. One disadvantage of the traditional differential arises because the torque distribution between the driven wheels is geometrically fixed. Thus, when one wheel spins on ice or mud, the torque provided to the other wheel was found to be insufficient to allow the vehicle to pull away.
In order to address this problem, limited-slip differentials were developed that have the capability of changing the speed difference between the driving wheels within a predetermined range. The typical limited-slip differential could operate as a conventional xe2x80x9copenxe2x80x9d, or equal torque, differential, or as a xe2x80x9clockedxe2x80x9d differential with no speed difference between the driving wheels, or anywhere between these extremes. Most limited-slip differentials use friction clutches between the differential input and output shafts to transmit at least a portion of the driving torque. In this category of limited-slip differentials, no torque is reacted outside the differential housing.
On the other hand, steering brakes for traction vehicles react driving torque through the vehicle chassis. Most traction vehicles do not have a traditional steering box, but instead rely upon deliberately altering the relative rotational speed between driving members to turn the vehicle. Like the steering brake system, certain wheel slip systems, usually referred to as xe2x80x9ctraction controlxe2x80x9d systems, also react torque outside the differential housing by actuation of the individual service brakes.
The conventional automotive drive train and differential system adequately serves the driving needs in most automotive applications. However, the utility of these same systems for high performance vehicles is inherently diminished. Due to the nature of operation of the typical differential, either fixed or limited slip, vehicle turning performance is limited. This problem is particularly pronounced in racing vehicles, where controlled high-speed turns are essential. There remains a need for a vehicle drive train system, and particularly for a differential system, that improves vehicle turning performance.
In order to address these needs, the present invention contemplates a yaw control system that can be integrated into an automotive drivetrain, particular at the differential. In one feature of the invention, the yaw control system includes a mechanism for applying a resistive torque to the axle of one of the driven wheels. In a preferred embodiment, the mechanism is a control brake operating on a flywheel or disc rotating with a drive wheel axle. Each control brake is hydraulically actuated, so the yaw control system contemplates a hydraulics system connecting the control brakes to a fluid source. Preferably, the fluid source is an engine-driven hydraulic pump.
In one important feature of the invention, each control brake is connected to the vehicle chassis to the resistive torque applied to the particular axle is reacted through the vehicle chassis. This torque reaction manifests itself as a yaw moment that augments the ability of the vehicle to negotiate a turn. To achieve this function, a further important feature of the invention includes an acceleration responsive control valve that selectively connects or disconnects the control brakes from the fluid source based on lateral acceleration of the vehicle as it travels through a turn. In this feature, the control valve includes an inertial or seismic mass that moves in the direction of the vehicle acceleration vector. The inertial mass is attached to a valve member that is operable to make a fluid connection between either control brake and the fluid source as the member is moved by movement of the inertial mass.
In a preferred embodiment, the valve member and inertial mass are pivotably mounted so that the valve member assumes a neutral position in which the control brakes are disconnected from the fluid source. When the vehicle turns, a lateral acceleration arises that moves the inertial mass to one side or another, thereby causing the valve member to pivot to a first or a second position alternately connecting one or the other control brake to the fluid source to activate the brake.
It is one object of the invention to facilitate and enhance the turning ability of an automotive vehicle, particularly a high performance or racing vehicle. It is another object to overcome some of the detriments of standard automotive differentials that reduce turning performance of a vehicle.
One benefit of the invention is that wheel slip is reduced in a tight turn, even for a vehicle having a constant torque differential. Another benefit is the functional attributes of the differential can be used to generate a turn-enhancing yaw moment within the vehicle. These and other objects and benefits provided by the present invention can be discerned from the following written description and accompanying figures.